Coin cleaning. When is it OK?

Is it okay to clean coins or not? There are mixed messages out there. On one hand, I have carefully broken through layers of crust on dirty roman bronzes to reveal details with the goal of identification. On the other hand, I have several badly tarnished silver ancient and medieval coins that are screaming to be cleaned, but I haven't given in to the temptation with the fear of greatly reducing the value as well as the authenticity. I'd really appreciate some thoughts on this.

 

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With crusty ancients, and to an extent medievals, it’s OK to clean them.

All ancients are cleaned in one form or another.

It’s how you clean them & with what that can be a potential issue.

Do a search within this ancient forum and you will find many threads on it.

 

I don't have any experience cleaning silver coins but I believe some folks do it with lemon juice. On the other hand with late roman bronze I have done quite a bit. Generally you can get some results by soaking the coins in distilled water for 48 hours and then scrubbing with a toothbrush to remove some of the dirt.

If that does not yield results than soak the coins in olive oil for some time (1 month at least - some folks keep them in olive oil for a year or two) then take out the toothbrush again. I also have used a dental pick to remove encrustations, doing so very carefully so as not to scratch the surface.

Other methods include electrolysis (which I am not experienced with) and liquid descaler. I tried liquid descaler on one lot of 50 coins and it destroyed virtually all of them (so I would not recommend it).

Anyway, it can be a fun process and you maybe discover some interesting coins. Classic finds include Constantinian bronzes such as the GLORIA EXERCITVS types, FEL TEMP REPARATIO types, SOLI INVICTO types, GLORIA ROMANORVM types, etc.
ranging from emperors like Constantine, through his sons (Crispus, Constantine II, Constans, and Constantius II), Julian, Jovian, Gratian, Valens, Theodosius, Arcadius, Honorius, and others.

 

Lemon juice is pretty mild and sometimes helps silver. I have used potassium hydroxide on some bronze.

 

The most important principle to learn about cleaning a coin is knowing when to quit. Sometimes it is best not even to start. That way you can quit while you are ahead.

 

Lemon juice should only be used for a few minutes at a time, and multiple soaks as needed. Don't just leave a coin unatended in it for hours. It will probably ruin the coin by leaching all the impurities and leaving the coin highly porous.

Look, with coins it is honestly better not to clean unless it's for identification purposes or the deposit is so heavy it ruins the aesthetics of the coin substantially. You are more liable to do damage to the coin than not. There is nothing wrong with having an occasional dark toned silver coin. I think they can be beautiful too. If anything, dark toning makes an ancient silver coin look more authentic. I don't think a 2,000 year old coin should be bright as a mirror.




Do whatever you want, but my advise is just leave it as is and learn to live with it before you end up irreversably damaging a perfectly good coin. I've seen a newbie here ruin a perfectly decent Gordian III ant by soaking it in lemon juice for several hours. By the time he was done, coin went from a dark beauty with excellent surfaces, to a shinny pile of turd with surfaces so porous no one would ever want that coin in their collection.

 

100% agreed. Unless it's completely uncleaned or has some heavy deposits on it, best leave it as is.

 

Cleaning ancient coins is exceptionally fun and rewarding personally and I'd highly recommend expanding your experience and repertoire of chemical and mechanical techniques. Using a 20x binocular microscope has opened my eyes to what is possible and is of paramount importance if you want to clean coins well. It's taken some trial and error plus lots of hands-on experience so while there is still much to be learned I'm now pretty good at spotting which cheap cruddy looking coins can be cleaned to reveal great pieces with good surfaces underneath the deposits (thus greatly enhancing value) and which ones to avoid because of telltale signs indicating that the patina and surfaces are a lost cause. For chemical treatments you should start with cheap modern silver and copper alloy coins to get a feel for what to expect before applying the same treatments to special medieval and ancient coins.

For example, in my opinion @Sallent 's 1st Roman coin could easily be cleaned with both value and visual appeal significantly improved as the patina is irregular and superficial and the exposed silver appears relatively solid, smooth and uncrystallized which would be the same for the surfaces under the crud, whereas the 2 nice Sicilian litrae are as good as they can be as-is because the removal of their thick sulfide patinas would strip detail and reveal unattractive and unnatural frosted surfaces. Learned that the hard way with an inexpensive black ancient coin, but to get good at making omelettes one usually has to break a few eggs.

It's largely a matter of personal differences, inclinations and abilities but the fact is that basically every ancient coin has been cleaned so I wanted to learn how to do it myself and make the coin budget stretch a bit further. Spending a few hours handling and cleaning a coin, studying every tiny detail under 20x magnification is an extremely intimate and personal way to experience a coin and make it one's own. And when you've taken an unrecognizable or obscured slug and revealed a lovely high-grade gem the feeling of satisfaction and accomplishment is sublime, it's almost as though you participated in the very creation of the piece.

 

You are almost tempting me to send you my Victoriatus to test your skills. I personally would never clean it myself, because I don't clean old silver (I don't mind toning or patina on ancient silver). But if you want to take a crack at it let me know.

 

Well, you aren't likely to impact the authenticity--the coin is either genuine or not, regardless of how clean it is. As for value, I wouldn't worry so much about that. Rather, consider the aesthetics: is the coin likely to be more or less pleasing if you clean it? Ancient coins are not like US coins in that respect; you don't automatically destroy its value just by cleaning it.

I've had a lot of experience cleaning coins. I've ruined a few in the process, and I've also had many successes, some quite spectacular.

I'd say it depends on the coin. You might post a picture of the coin or coins that you are considering cleaning. Then we can give you more specific advice about whether/how to proceed. Of course, the answers will be all over the map, but at least we'll know what specific coin and preservation state we're pontificating about.

 

@gsimonel the key word is that you ruined a few coins. With ancients, it's not like they are making them anymore, so ruining a few coins is not a legacy I'd like to leave to future would-be collectors.

I'm hoping it was an uncleaned lot and the coins you ruined were a few late bronzes that were already somewhat in rough shape. I'd hate to think you ruined a nice silver coin just because you wanted it to be all shinny like new.

 

I love my ancient coin collection--the history, the beauty, the challenge of tracking down certain coins--but the reality is that they are just old lumps of metal. No one dies or starves to death if I ruin an ancient coin.

In most cases, the few coins I've ruined were already in terrible shape, but they ended up losing detail after I subjected them to electrolysis--perhaps a dozen or so coins out of the hundreds whose appearance improved by the same process.

There was one nicer, silver coin that ended up looking worse after treatment, though, which I regret. It was an unidentifiable, thick, black slug when I received it in a lot of uncleaned coins. I had no idea it was silver. It did not respond to any of the less-harsh cleaning methods that I tried, so I subjected it to electrolysis and discovered a scarce denarius of Vespasian. There was a lot of good detail, but its appearance was marred by dark, patchy black stains left by the encrustation. I wanted to lighten or remove the stains if possible. This was many years ago, when I was still somewhat new at the hobby and hadn't had any experience cleaning silver coins. I was told it was safe to use lemon juice on Vespasian-era silver, so I let it soak overnight. Turns out it was a provincial coin of lower-quality silver. The coin came out cleaner but with a lot of porosity, and it retrospect it probably would have looked better had I left the black patches on it.

Here then is my true confession:

Vespasian
Augustus, A.D. 69-79
Provincial Silver Denarius
Phillipi mint, A.D. 69-70
Obv: IMP CAES VESPAS AVG
Rev: PACI OPB TERR AVG - Turretted female bust
Φ behind bust
RIC (New) 1407
18mm, 2.8g.

 

I’ve cleaned a few times in the past, but of those here are my two favorites.

Louis the Pious, Carolingian Empire/Republic of Venice
AR denier
Obv: +HLVDOVVICVS IMP, legend around cross in circle
Rev: +VEN / ECIAS, legend in two lines
Mint: Venice
Date: 818-840 AD
Ref: MG 456v, MEC 789





Tiberius, Roman Empire
AR denarius
Obv: TI CAESAR DIVI AVG F AVGVSTVS, laureate head right
Rev: PONTIF MAXIM, Livia (as Pax) seated right, holding long scepter in her right hand and olive branch in her left; plain chair legs
Mint: Lugdunum
Date: 14-37 AD
Ref: RIC 26





For pure/nearly pure silver, ammonia (preferably mixed with some distilled water) works well for tough, hard gunk.

 

This is why I always tell people to stop using lemon juice, unless it is a controlled process of short 10-20 minute soaks followed by close examination of the coin. A lot of good coins have been ruined by being left to soak in lemon juice overnight. The acid will leach all the copper from the coin, leaving a highly porous and fragile coin. When using an acidic solution on an ancient coin, it is not a drop and forget operation. It is a drop briefly, inspect closely, and repeat only as needed type of operation.

 

I do not clean. Why risk destroying History?

 

"This is why I always tell people to stop using lemon juice, unless it is a controlled process..."

Acids are a bad idea for cleaning ancient coins. Period. It "works" by dissolving both metal and dirt. That it works faster on the dirt doesn't mean that it's not doing some harm to the coin itself too. Silver is not very reactive chemically but remember that silver coins are not 100% pure. They contain varying amounts of other elements which do tend to be more susceptible. When acid attacks a coin along with the dirt it also takes away some of those secondary elements leaving behind a more matte appearance or a downright pitted one if the overall silver content is low.

You would never find a museum or an auction house using home remedies like lemon juice or vinegar to clean their coins so why would you? The best method remains cleaning under a low-power microscope. This is how they do it.

Rasiel

 

You would be shocked by standard archaeology lab methods...

 

Unfortunately, I learned this the hard way. What can I say, I was just starting out. If I need to clean a silver coin now--which is very rare--I use a Q-tip (cotton swab) dipped in lemon juice followed by a distilled water soak to remove all trace of the acid.

 

I would go as non-abrasive as possible and work my way up. So maybe distilled water soaks and gentle rubbing. Then olive oil soaks.

I just completed my first attempt at lightly cleaning some silver. Using baking soda, boiling water, and aluminum foil I took away some of the less eye appealing toning on this Caracalla denarius.



We have members here who have done some amazing stuff removing the hard deposits with much eye appealing success. Pick their brains for sure.

Less is more just go slowly.

 

As others have mentioned, all ancient coins have been cleaned to some extent. Some collectors value bright, shiny coins but I personally prefer my coins to look old. That means some toning, the odd flan crack, and sometimes the odd encrustation as long as it doesnt obscure important details.
Just be very careful not to ruin a coin.
IMO the only things that are unacceptable are completely depatinating a bronze coin, and leaving behind scratches or surface degradation (on bronze or silver) from overly aggresive cleaning methods; mechanical or chemical.
This is a patient person's game, and for the most part I'd say buy coins that are already in the state you would like.

For what it's worth, my own experience in coin cleaning is limited. I have given a couple of silver coins a light lemon juice q-tip rub just to brighten and bring forward the high points. I am no expert thats for sure =)